Maps

Using Maps with GPS : Using Maps with GPS GPS for ICS - 2003


Using Maps with GPS : Objectives: Explain the purpose of datums. Identify the two “global” coordinate systems most commonly used with GPS. Describe “datum shift,” and the relevance it has when using GPS in the field. Describe the four components that make up UTM coordinates. Identify the three ways that lat/long coordinates can be expressed. Successfully plot or locate four points on a map in lat/long, and four points in UTM. Using Maps with GPS


Projecting a Sphere Onto a Plane : Projecting a Sphere Onto a Plane Three-dimensional sphere to two-dimensional flat map.


Examples of Several Projections : Examples of Several Projections Depending on the projection, a certain amount of distortion occurs when portraying the earth on paper.


Projections and Datums : Projections and Datums


Datum Shift : Datum Shift


Datum Shift : Datum Shift


Maps : A map is a two-dimensional representation of the earth. Maps incorporate projections and datums to provide a way to reference locations on the map to features on the ground (via coordinate systems). All maps distort the earth to some extent. Many different types of maps can be used with GPS. When using a GPS receiver with a map, the datum and coordinate system in the receiver must match the map datum. Maps


Example of a USGS Map Legend : Mapped, edited, and published by the Geological Survey Control by USGS USC&GS Topography from aerial photographs by multiplex methods and by plane-table surveys 1953. Aerial photographs taken 1951 Polyconic projection. 1927 North American Datum 10,000 foot grid based on Idaho coordinate system, west zone 1000-meter Universal Transverse Mercator grid ticks, 1000-meter Universal Transverse Mercator grid ticks, zone 11, shown in blue To place on the predicted North American Datum 1983 move the projection lines 15 meters north and 77 meters east as shown by dashed corner ticks UTM GRID AND 1971 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET Example of a USGS Map Legend


Coordinate Systems : All coordinate systems reference some particular set of numbers for the size and shape of the earth (the datum). Coordinate systems are used to designate locations within a datum. There are two types of global coordinate systems: Angular coordinate system Rectangular (Cartesian) coordinate system Latitude and longitude, and Universal Transverse Mercator are two global coordinate systems commonly used by GPS users. Many other coordinate systems exist worldwide. Coordinate Systems


Slide11 : Coordinate Systems hddd0 mm’ ss.s”: N 430 40’ 55.8” X W 1160 17’ 14.1” (55.8” / 60 = .93’) Different coordinates representing the same location: UTM/UPS: 11T 0557442m E 4836621m N


Precision vs Accuracy : Precision and accuracy are not the same. Precision refers to how small an area coordinates can be defined or plotted. GPS lat/long coordinates can be defined to 1/10 of a second. UTM coordinates can be defined down to one meter. Accuracy refers to how closely a GPS receiver can calculate its position relative to its true location. GPS accuracy can vary from a few millimeters to several kilometers. Precision vs Accuracy


Latitude & Longitude : Latitude & Longitude


Latitude & Longitude : A geographic (spherical) coordinate system. Angular coordinates are perfectly suited to the ellipsoidal shape of the earth. Coordinates are expressed in degrees, minutes and seconds (and variations of that). Position coordinates are based on an angular distance from a known reference point. That reference point is where the Prime Meridian and equator intersect. Lat/long is the predominant coordinate system used for nautical and aeronautical navigation. Latitude & Longitude


Latitude & Longitude : Latitude & Longitude


Latitude & Longitude : Latitude & Longitude


Latitude : Latitude is comprised of parallels, which are equally spaced circles around the earth paralleling the equator. Parallels are designated by their angle north or south of the equator (10º, 20º, etc) . The equator is 0º latitude, and the north and south poles are at 90º angles from the equator. The linear distance between parallel (latitude) lines never changes, regardless of their position on the earth. Latitude


Parallels of Latitude : Parallels of Latitude 10º 10º 10º 690 miles 690 miles 690 miles 10º S 0º N 10º N 20º N


Longitude : Longitude is comprised of meridians that form one-half of a circle, or plane. Meridians are designated by their angle west or east of the prime meridian. The prime meridian is designated 0º and extends from the north pole to the south pole through Greenwich, England. Meridians are angled, and do not parallel each other. The linear distance between one degree of longitude at the equator is approximately 69 statute miles. The linear distance between one degree of longitude at the arctic circle is only about 26 statute miles. Longitude


Meridians of Longitude : Meridians of Longitude 10º 10º 110º W 120º W 690 miles 460 miles 240 mi 10º Equator To North Pole To South Pole


Determining Latitude & Longitude : Determining Latitude & Longitude 50º W 30ºN, 50ºW


Determining Latitude : Determining Latitude


Determining Longitude : Determining Longitude Longitude of red square = 115º 19’ 00”


Universal Transverse Mercator : Is a rectangular (planar) coordinate system based on the latitude and longitude (geographic) coordinate system. The earth is divided into 60 UTM zones. Sixty zones allows the earth to be projected onto maps with minimal distortion. UTM uses “false” values (easting and northing) to express coordinates. Coordinates are expressed in meters. Universal Transverse Mercator


UTM Coordinates : 11T 0541450 4789650 UTM Coordinates


UTM Coordinates : 1450 9650 11T 05 47 4 8 UTM Coordinates You need only plot the black numbers on the map. The rest of the coordinate values are provided for you by the map.


UTM Grid Overlay : 1 60 UTM Grid Overlay 60 Zones, and 20 Latitude Bands Zones Equator


UTM Zones in the Contiguous U.S. : UTM Zones in the Contiguous U.S.


UTM Zones - Side by Side : UTM Zones - Side by Side


UTM Uses a Cartesian Grid : UTM Uses a Cartesian Grid


Plotting UTM Coordinates : Plotting UTM Coordinates House coordinates = 0541450mE 4789650mN UTM grid reader Place the corner of the UTM grid reader on the point to be plotted 542 543 4790 4791 1,000 m Each tic = 100 meters on this grid reader (your grid reader has 20 meter tics)


Using GPS with Maps : Lesson objectives revisited: Explain the purpose of a datum. Identify the two “global” coordinate systems most commonly used with GPS. Describe “datum shift,” and the relevance it has when using GPS in the field. Describe the four components that make up UTM coordinates. Identify the three ways that lat/long coordinates can be expressed. Successfully plot or locate four points on a map in lat/long, and four points in UTM. Using GPS with Maps